The present invention relates to a steel sheet used for preparing a heat shrink band for fastening the periphery of a panel portion in a color cathode ray tube such as a television receiver, particularly, to a steel sheet for a heat shrink band that is effective for preventing the color drift.
In a color cathode ray tube, the inner space of the tube is held at a high vacuum state of 1.0xc3x9710xe2x88x927 Torr. Therefore, in order to prevent the deformation of the panel face and the implosion of the tube body, a heat shrink band made of a steel sheet that is formed into a band is arranged in the periphery of the panel portion so as to impart tension to the periphery of the panel portion and, thus, to correct the deformation of the panel face.
Further, the heat shrink band performs the function of shielding the geomagnetism as well as the function of shielding the internal magnetism so as to prevent the landing position of the electron beam on the phosphor screen from being deviated by the geomagnetism. In other words, the heat shrink band also performs the function of preventing the color drift.
A soft steel sheet has been used for preparing the heat shrink band. However, in the case of using a soft steel sheet, the geomagnetic drifting properties are relatively large, leading to a low degree of allowance in respect of the color drift inhibition. Such being the situation, it is strongly required to develop a material capable of effectively preventing the color drift.
An object of the present invention is to provide a steel sheet for preparing a heat shrink band small in the geomagnetic drift and effective for preventing the color drift while maintaining tension favorably comparable with that of the conventional steel sheet.
According to an aspect of the present invention, there is provided a steel sheet for preparing a heat shrink band effective for preventing the color drift, wherein said steel sheet has 24 kg/mm2 or higher of yield stress and at least 400 or higher of the product between the permeability xcexc under a magnetic field of 0.3 Oe and the sheet thickness.
According to another aspect of the present invention, there is provided a steel sheet for preparing a heat shrink band effective for preventing the color drift, wherein said steel sheet contains 0.005% by weight or less of C, 0.005% by weight or less of N, 0.1% by weight or less of P, 0.02% by weight or less of S, 0.2 to 3.0% by weight of Si, 1.0% by weight or less of Mn, and 1.0% by weight or lsess of sol. Al, and has 24 kg/mm2 or higher of yield stress and 400 or higher of the product between the permeability xcexc under a magnetic field of 0.3 Oe and the sheet thickness.
As a result of an extensive research conducted in an attempt to achieve the objects noted above, the present inventors have found that:
(1) The color drift can be improved, if the product xcexcxc3x97t of the raw material steel sheet for a band is 400 or higher, where xcexc represents the permeability under an external magnetic field intensity of 0.3 Oe, which is equal to the geomagnetic level, and t represents the thickness of the steel sheet; and that:
(2) It is necessary to add 0.2% by weight or higher of Si to the steel sheet raw material in order to allow the steel sheet to exhibit strength equal to or higher than that of the conventional steel sheet while maintaining the permeability noted above.
The present invention has been achieved on the basis of these findings.